This invention relates generally to radio frequency energy detection circuitry and more particularly to circuitry of such type which is adapted to respond to the detection of radio frequency energy but which is non-responsive to small fades in the power level of the radio frequency energy under detection.
As is known in the art, it is frequently required to provide radio frequency energy detection circuitry. Such circuitry typically includes a diode detector to, in effect, rectify received radio frequency energy and thereby produce a detected signal representing the power in the received radio frequency energy. The output of the diode detector is sometimes fed to a first input of a comparator, the second input of the comparator being fed by a signal representative of a threshold level. In the absence of the received radio frequency energy, the output of the comparator is at an initial state; however, when radio frequency energy is received having a power level greater than that represented by the threshold level, the threshold level at the second input of the comparator is exceeded, thereby changing the logic state at the output of the comparator from the initial state to a second state. When the received radio frequency energy terminates, the level at the first input of the comparator falls below the threshold level returning the output state of the comparator to its initial state.
While such arrangement is adequate for many applications, in some applications the received radio frequency energy may momentarily fade to a level below that corresponding to the threshold level at the second input of the comparator, thereby changing the output state of the comparator from the second state back to the initial state. In some applications, however, it may be undesirable for the circuitry to respond to these momentary fades but rather it is desirable that the circuitry continue to indicate the presence of received radio frequency energy and thus prevent the detection circuitry from responding to these false losses of radio frequency energy indications.